<template>
  <div class="pagination">
    <button>上一页</button>
    <button v-show="startAndEnd.start > 1" @click="changePageNo(1)">1</button>
    <span v-show="startAndEnd.start > 2">...</span>
    <button
      v-for="(_, index) in startAndEnd.end - startAndEnd.start + 1"
      :key="_"
      :class="{ active: startAndEnd.start + index == pageNo }"
      @click="changePageNo(startAndEnd.start + index)"
    >
      {{ index + startAndEnd.start }}
    </button>

    <button v-show="startAndEnd.end < totalPage - 1">···</button>
    <button
      v-show="startAndEnd.end < totalPage"
      @click="changePageNo(totalPage)"
    >
      总页数:{{ totalPage }}
    </button>
    <button @click="changePageNo(pageNo + 1)" :disabled="pageNo === totalPage">
      下一页
    </button>

    <span style="margin-left: 30px">共 {{ total }} 条</span>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ["total", "pageNo", "pageSize", "continues", "changePageNo"],
  computed: {
    //计算页码总数
    totalPage() {
      const { total, pageSize } = this;
      return Math.ceil(total / pageSize);
    },
    // 计算起始结束页
    startAndEnd() {
      const { pageNo, continues, totalPage } = this;
      let start, end;
      if (continues > totalPage) {
        start = 1;
        end = totalPage;
      } else {
        start = pageNo - parseInt(continues / 2);
        end = pageNo + parseInt(continues / 2);
        //考虑正常情况的另外两种情况
        // 1如果初始页小于1
        if (start < 1) {
          start = 1;
          end = continues;
        }
        // 2如果结束页大于总页码
        if (end > totalPage) {
          //结束页必须是totalPage
          end = totalPage;
          // 开始页要从后往前算
          start = totalPage - continues + 1;
        }
      }
      return { start, end };
    },
  },
};
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #c81623;
      color: #fff;
    }
  }
  span {
    display: inline-block;
    line-height: 28px;
    font-size: 14px;
    color: gray;
    vertical-align: middle;
  }
}
</style>